netfilter: nf_flow_table: fix big-endian integer overflow

Message ID 20191210202443.2226043-1-arnd@arndb.de
State Accepted
Commit c9b3b8207bc487de02cbca968927ba2c2cb46aaf
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Series
  • netfilter: nf_flow_table: fix big-endian integer overflow
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Commit Message

Arnd Bergmann Dec. 10, 2019, 8:24 p.m.
In some configurations, gcc reports an integer overflow:

net/netfilter/nf_flow_table_offload.c: In function 'nf_flow_rule_match':
net/netfilter/nf_flow_table_offload.c:80:21: error: unsigned conversion from 'int' to '__be16' {aka 'short unsigned int'} changes value from '327680' to '0' [-Werror=overflow]
   mask->tcp.flags = TCP_FLAG_RST | TCP_FLAG_FIN;
                     ^~~~~~~~~~~~

From what I can tell, we want the upper 16 bits of these constants,
so they need to be shifted in cpu-endian mode.

Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
I'm not sure if this is the correct fix, please check carefully
---
 net/netfilter/nf_flow_table_offload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.20.0

Comments

Pablo Neira Ayuso Dec. 20, 2019, 1:10 a.m. | #1
On Tue, Dec 10, 2019 at 09:24:28PM +0100, Arnd Bergmann wrote:
> In some configurations, gcc reports an integer overflow:

> 

> net/netfilter/nf_flow_table_offload.c: In function 'nf_flow_rule_match':

> net/netfilter/nf_flow_table_offload.c:80:21: error: unsigned conversion from 'int' to '__be16' {aka 'short unsigned int'} changes value from '327680' to '0' [-Werror=overflow]

>    mask->tcp.flags = TCP_FLAG_RST | TCP_FLAG_FIN;

>                      ^~~~~~~~~~~~

> 

> From what I can tell, we want the upper 16 bits of these constants,

> so they need to be shifted in cpu-endian mode.

> 

> Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>


Applied, thanks.

Patch

diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
index c54c9a6cc981..24543c45d501 100644
--- a/net/netfilter/nf_flow_table_offload.c
+++ b/net/netfilter/nf_flow_table_offload.c
@@ -77,7 +77,7 @@  static int nf_flow_rule_match(struct nf_flow_match *match,
 	switch (tuple->l4proto) {
 	case IPPROTO_TCP:
 		key->tcp.flags = 0;
-		mask->tcp.flags = TCP_FLAG_RST | TCP_FLAG_FIN;
+		mask->tcp.flags = cpu_to_be16(be32_to_cpu(TCP_FLAG_RST | TCP_FLAG_FIN) >> 16);
 		match->dissector.used_keys |= BIT(FLOW_DISSECTOR_KEY_TCP);
 		break;
 	case IPPROTO_UDP: